This project proposes a study of the circadian rhythms of cortisol and alpha-amylase and their relationship to tonic pupil size in two to five year old children with Autism Spectrum Disorder. The aim of the current application is to explore non-invasive measures of both the hypothalamic and norepinephrine systems to determine their involvement in producing atypical autonomic responses in children with autism. In addition, this proposal seeks to determine whether such measures could provide insight into potential neural impairment in autism, and if these measures could eventually be used to identify the disorder early in life. The tasks include measurement of (a) pupil size at rest, and (b) daytime variations in salivary measures of cortisol and alpha-amylase across two days. Atypical baseline levels of autonomic activity and sleep difficulties have been previously reported in persons with autism and indicate a heightened level of sympathetic activity. However, pupillary responses have been found to be more reliable and less influenced by noise than other autonomic measures such as heart rate. In addition, pupil size has recently been found to be larger at rest and smaller to human faces in two to five year old children with autism than controls. Both the hypothalamic and norepinephrine systems contribute to the control of the autonomic nervous system and help to maintain appropriate levels of alertness to prepare the CNS to respond to incoming information. Persons with autism have been found to have heightened levels of norepinephrine and lower levels of cortisol, but these responses have been suggested to be atypical due to heightened stress associated with blood draw. Therefore, measurement of the salivary correlates of the norepinephrine and hypothalamic systems, alpha-amylase and cortisol respectively, provide a non-invasive measure of these systems. Pilot data are presented that show the discriminant ability of the measurement of alpha-amylase throughout the waking state. These measures will be taken on two separate days on a group of 20 children with a diagnosed Autism Spectrum Disorder, 20 children with Down Syndrome, and 20 typically-developing children. PUBLIC HEALTH RELEVANCE: This project seeks to determine the neurochemical systems involved in producing the atypical autonomic responses in autism, and thus provides two potential contributions to public health. First, the autonomic and salivary measures could provide potential early markers of autism, as these non-invasive measures could be used during infancy to determine the probability of developing the disorder. Second, determination of the neurochemical component responsible for atypical autonomic responses could lead to identification of a neural impairment in autism that is potentially primary to other impairments, and could lead to pharmacological and/or behavioral interventions targeted at preventing this impairment from causing a cascade of effects.